Snippet of RSA accumulator which demonstrates adding a value to a set

AddToAccumulator.kt

fun add(x: BigInteger): RSACommit {
    return if (data.containsKey(x)) {
        commitment
    } else {
        val (hashPrime, nonce) = hashToPrime(x, ACCUMULATED_PRIME_SIZE)
        commitment = commitment.modPow(hashPrime, n)
        data[x] = nonce
        commitment
    }
}

fun hashToPrime(x: BigInteger, bitLength: Int = 120, initNonce: BigInteger = BigInteger.ZERO): TwoValue<BigInteger> {
    var nonce = initNonce
    while (true) {
        val num = hashToLength(x + nonce, bitLength)
        if (num.isProbablePrime(primeCertainty)) {
            return TwoValue(num, nonce)
        }
        nonce += BigInteger.ONE
    }
}

fun hashToLength(x: BigInteger, bitLength: Int): BigInteger {
    var hexString = ""
    val numOfBlocks = Math.ceil(bitLength / 256.00).toInt()
    for (i in 0 until numOfBlocks) {
        hexString += sha256.hashBytes((x + i.toBigInteger()).toString(10).toByteArray()).asBytes()
            .toHexString()
    }

    if (bitLength % 256 > 0) {
        // # we do assume divisible by 4
        hexString =
            hexString.substring((bitLength % 256) / 4)
    }
    return BigInteger(hexString, 16)
}